This trigger is bolted to the rubber donut at either the diff or the gearbox.
Most T56/TR6060 Tremec 6 speed boxes don't have a hole for the speedo drive/sensor. This trigger wheel spins with the tailshaft to simulate a speedo drive. You can use the two-wire sensor from the A340 auto box and mount it near the trigger wheel.
Then run two wires into the cabin through the gear lever hole. connect these wires to a Dakota digital speed speedo controller (NOT INCLUDED).
 
Watch this video for fitting instructions https://youtu.be/UBd6RuxSpUc
Approx 22:00 minutes in.